Methanation and Recovery Method, System, and Apparatus

ABSTRACT

A method, a system, and an apparatus of certain embodiments are provided to recover water and carbon dioxide from combustion emissions. The recovery includes, among other things, electrolysis and carbon dioxide capture in a suitable solvent. The recovered water and carbon dioxide are subject to reaction, such as a catalytic methanation reaction, to generate at least methane.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM(S) OF PRIORITY

This application is a divisional of U.S. patent application Ser. No.17/528,587 filed Nov. 17, 2021, now allowed, the complete disclosure ofwhich is hereby incorporated by reference.

BACKGROUND

Embodiments disclosed herein relate to methods, systems, and apparatusesfor carrying out methanation and recovering and/or reclaimingmethanation reactants from a combustion exhaust stream. Certainembodiments disclosed herein relate to methods, systems, and apparatusesfor carrying out scrubbing, electrolysis, and thermal exchangeoperations in a common tank or chamber. Certain embodiments disclosedherein involve operations including carbon dioxide absorption anddesorption. Certain exemplary embodiments involve the efficient use andtransfer of heat between different operations.

Signatories to the Paris Climate Agreement are committed to steepreductions in greenhouse gas emissions, which include carbon dioxide,over the coming decade. The technological and economic challenge ofmeeting emission reductions under the Paris Climate Agreement isextremely significant. Fossil fuel-reliant industries such as powergeneration and manufacturing that output high levels of greenhouse gasemissions are especially vulnerable to new regulations that are rapidlyreducing their profitability.

One solution for meeting the goals of the Paris Climate Agreement isrenewable energy. Renewable energy is cheap and abundant when and whereit is available. One of the problems with renewable energy sources isthat the sources are not always available or plentiful. Unlike fossilfuels, which are dispatchable on demand to produce electricity or heatfor satisfying consumer and business energy needs, photovoltaic (PV)solar power renewable energy is plentiful for typically less than 40% ofthe time, i.e., during peak sunlight hours. Wind turbines depend onenvironmental wind as a natural renewable energy resource; wind speedscan fluctuate greatly over the course of a day and adequate wind speedsare not abundant in many locales. Accordingly, the complete supplantingof non-renewable energy sources with renewable energy is, at the presenttime, likely infeasible given the world energy demands.

SUMMARY

This Summary is provided to introduce a selection of representativeconcepts in a simplified form, which representative concepts are furtherdescribed below in the Detailed Description. This Summary is notintended to identify key features or essential features of the claimedsubject matter, nor is it intended to be used to limit the scope of theclaimed subject matter.

In an embodiment, a method includes receiving a hydrocarbon combustionexhaust stream including at least water and carbon dioxide in a chambercontaining liquid water. The liquid water in the chamber, in anexemplary embodiment including water condensed from the exhaust stream,is subject to electrolysis to generate hydrogen and oxygen. Methanationreaction products are conveyed through one or more heat exchangers inthe chamber to transfer heat from the methanation reaction products tothe liquid water.

In another embodiment, a method includes subjecting liquid water in achamber to electrolysis to generate hydrogen and oxygen, capturingcarbon dioxide in a solvent, and conveying the solvent and the capturedcarbon dioxide through a first heat exchanger of the chamber.Methanation reaction products are conveyed through the a second heatexchanger, which may be the same as or different than the first heatexchanger, of the chamber to transfer heat from the methanation reactionproducts to the liquid water in the chamber and to the solvent withcaptured carbon dioxide conveyed through the first heat exchanger of thechamber.

In still another embodiment, a method includes receiving a hydrocarboncombustion exhaust stream including at least water and carbon dioxide ina chamber containing liquid water. The liquid water, in an exemplaryembodiment including water condensed from the combustion exhaust stream,in the chamber is subjected to electrolysis to generate hydrogen andoxygen. Methanation reaction products are passed through a heatexchanger of the chamber to transfer heat from the methanation reactionproducts to the liquid water. Carbon dioxide is captured in a solvent,and the solvent with the captured carbon dioxide is heated in the sameor a different heat exchanger of the chamber. At least a portion of thecarbon dioxide is separated from the heated solvent. The hydrogengenerated by the electrolysis and the carbon dioxide separated from theheated solvent are reacted in a methanation reactor to generate one ormore hydrocarbons, such as methane.

In a further embodiment, a system includes a chamber, an electrolysissystem, and one or more heat exchangers. The chamber is configured tocontain liquid water and to receive a hydrocarbon combustion exhauststream including at least water and carbon dioxide. The electrolysissystem is configured to generate hydrogen and oxygen, and includes atleast an anode and a cathode each received in the chamber. The one ormore heat exchangers is/are positioned in the chamber and configured toconvey methanation reaction products through the chamber to transferheat from the methanation reaction products to the liquid water.

In still a further embodiment, a system includes a chamber, a carbondioxide absorber, and first and second heat exchangers. The chamber isconfigured to subject liquid water to electrolysis to generate hydrogenand oxygen. The carbon dioxide absorber is configured to capture carbondioxide in a solvent. The first heat exchanger is positioned in thechamber and configured to convey the solvent and the captured carbondioxide through the chamber. The second heat exchanger, which may be thesame as or different than the first heat exchanger, is positioned in thechamber and configured to convey methanation reaction products throughthe chamber to transfer heat from the methanation reaction products tothe liquid water in the chamber and to the solvent with captured carbondioxide being conveyed through the first heat exchanger of the chamber.

According to another embodiment, a system includes a chamber configuredto contain liquid water and to receive a hydrocarbon combustion exhauststream including at least water and carbon dioxide. An electrolysissystem comprising an anode and a cathode positioned in the chamber isconfigured to generate hydrogen and oxygen from the liquid water. Afirst heat exchanger is positioned in the chamber and configured toconvey methanation reaction products through the chamber to transferheat from the methanation reaction products to the liquid water. Acarbon dioxide absorber is configured to capture the carbon dioxide in asolvent. A second heat exchanger, which may be the same as or differentthan the first heat exchanger, is positioned in the first chamber andconfigured to heat the solvent and the captured carbon dioxide withthermal energy from the methanation reaction products. A carbon dioxidedesorber is configured to separate at least a portion of the carbondioxide from the heated solvent. A methanation reactor is configured toreact at least the hydrogen generated by the electrolysis system and thecarbon dioxide separated from the heated solvent to generate one or morehydrocarbons.

Other aspects of the invention, including apparatus, devices, systems,sub-systems, assemblies, sub-assemblies, processes, methods, and thelike, which constitute part of the invention, will become more apparentupon reading the following detailed description of the exemplaryembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. Features shown in the drawings are meant asillustrative of only some embodiments, and not of all embodiments,unless otherwise explicitly indicated. In such drawings:

FIG. 1 is a schematic flow diagram of a system according to an exemplaryembodiment;

FIG. 2 is a flow chart of a method according to an exemplary embodiment;

FIG. 3 is a schematic diagram of an embodiment of a SET/separator tankaccording to an exemplary embodiment;

FIG. 4A is a cross sectional view taken along sectional line 4A-4A ofFIG. 4B of an apparatus according to an exemplary embodiment;

FIG. 4B is a cross-sectional view taken along sectional line 4B-4B ofthe apparatus of FIG. 4A;

FIG. 5 is a schematic diagram of a methanation system according to anembodiment;

FIG. 6 is a flowchart of a method of operating the methanation system ofFIG. 5 ; and

FIG. 7 is an illustrative example of a makeup of electricity generatorsources for providing energy to a given geographical error (e.g., NewYork State) at a given day and time.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS AND EXEMPLARY METHODS

It will be readily understood that the components, structures, andfeatures of the present embodiments, as generally described andillustrated in the Figures incorporated herein, may be arranged anddesigned in a wide variety of different configurations. Thus, thefollowing detailed description of the embodiments of the apparatus,system, and method of the present embodiments, as presented in theFigures, is not intended to limit the scope of the embodiments, asclaimed, but is merely representative of selected embodiments.

Reference throughout this specification to “a select embodiment,” “anembodiment,” “an exemplary embodiment,” “one embodiment,” or “at leastone embodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least an embodiment. Thus, appearances of the phrases “a selectembodiment,” “an embodiment,” “an exemplary embodiment,” “in oneembodiment,” or “in at least one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment or different embodiments. The various embodiments may becombined with one another in various combinations that would beunderstood to those skilled in the art having reference to thisdisclosure.

The illustrated embodiments will be best understood by reference to thedrawings, wherein like parts are designated by like numerals throughout.The following description is intended only by way of example, andillustrates certain selected embodiments of systems, processes, andapparatuses that are consistent with the certain selected embodiments.

Exemplary embodiments are now described with respect to a system (100)of FIG. 1 and a process (200) of FIG. 2 .

In step (202) of the flowchart (200) of FIG. 2 , a hydrocarboncombustion exhaust stream that has undergone at least partial (orsubstantially complete or complete) combustion is received. The streammay originate from various resources, such as, without limitation, oneor more hydrocarbon combustion appliances and/or plants, such as anelectricity generation plant. Combustion of hydrocarbons is the basisfor most processes and systems that underpin modern economies.Combustion equipment includes, but is not limited to, boilers forproducing hot water and steam, furnaces for producing hot air, internalcombustion engines for vehicles in transportation, turbines for powergeneration and jet propulsion, rocket nozzles for missile and spacecraftthrust, industrial kilns, smelting processes for producing steel, etc.These apparatuses exhaust mixtures typically including carbon dioxide,water, nitrogen, trace gases (e.g., carbon monoxide, nitrogen oxides,sulfur oxides, argon, etc.), or combinations thereof, and particulatematter (e.g., soot), typically as a result of combustion. Carbon dioxideand water typically compose, for example, more than 99% by mass of thetotal mass of the non-nitrogen portion of the exhaust during thecombustion of hydrocarbons and air. Carbon monoxide may be present insignificantly smaller quantities depending on the excess air ratio usedduring combustion. The ratios may vary according to the combustionprocess and input material.

The system (100) of FIG. 1 includes a combustion reactor or otherappliance (102) from which an exhaust stream (also referred to herein asa combustion stream and the like) (104) is received. The combustionappliance (102) typically burns a hydrocarbon such as methane in thepresence of an oxygen source such as air, emitting the exhaust stream(104) typically containing carbon dioxide, nitrogen, and water, whichmay be present in various physical forms, such as steam, vapor, andliquid, but typically is mostly if not entirely gaseous. Exemplaryembodiments are designed to handle mixed exhaust streams comprising someor all of the constituents described above and other constituents, e.g.,particulate matter.

According to an embodiment, the exhaust stream (104) leaves thecombustion appliance (102) and is received in step (202) at atemperature of, for example, approximately 100° C. to 350° C., such as,for example about 250° C. The exhaust stream (104) typically containsgaseous water in an amount of, for example, as much as 10 percent bymass based on the total mass of the exhaust stream (104).

The exhaust stream (104) is introduced into a tank or the like,generally designated by reference numeral (106), also referred to hereinas a SET/separator tank (106). The SET/separator tank (106) contains afirst (shown as a lower) chamber (or compartment) (108), also referredto herein as the SET chamber or the SET tank, and a second (shown as anupper) chamber (or compartment) (110), also referred to herein as themethane separation chamber or the methane separation tank. For thepurposes of this application, SET is an acronym that stands forScrubbing, Electrolysis, and Transfer of heat.

The SET chamber (108) and the methane separation chamber (110) arepartitioned by a non-permeable partitioning wall (112), which is shownextending horizontally in FIG. 1 , but may possess other orientations.The partitioning wall (112) includes an injection tube or port (114)that fluidly communicates the SET chamber (108) and the methaneseparation chamber (110) with one another. While the SET chamber (108)and the methane separation chamber (110) are shown in FIG. 1 as beingpart of a common, that is the same, equipment or tank (106), in anotherembodiment the SET chamber (108) and the methane separation chamber(110) may be embodied as different pieces of equipment, such as a SETtank and a separate and discrete separator tank. Alternatively, thepositioning of the chambers (108) and (110) may be reversed or switchedwith respect to one another.

FIG. 1 illustrates the exhaust stream (104) being fed into the SETchamber (108) containing a liquid (115), which in an exemplaryembodiment includes or is composed of water. As shown, in an embodimentthe exhaust stream (104) is fed into a space (also referred to as aheadspace) of the SET chamber (108) above a liquid level line (116). Inembodiments, the liquid (115) establishing the liquid level line (116)includes or is substantially entirely water, optionally containing otherliquids and/or particulate matter (e.g., soot) from the exhaust stream(104). The liquid (115) in the SET chamber (108) may include othermaterials, such as solids (e.g., particulates) and buffers (e.g., KOH),e.g., for counteracting pH changes caused by acids, if any, formed fromcomponents of the exhaust stream (104). The particulate matter istrapped or entrained within the liquid (115), and may be removed viaperiodic cleaning.

The SET chamber (108) further includes a spray mechanism (118), a firstheat exchanger (120), a second heat exchanger (122), and an electrolysiscell (unnumbered in FIG. 1 ) including an electrolysis anode (124), anelectrolysis cathode (126), and a controller (125). The first and secondheat exchangers (120) and (122), respectively, may be separate heatexchangers or a common (i.e., the same) heat exchanger, as shown, forexample, in the embodiment of FIG. 3 , discussed below. The terms“first” and “second” in this regard are not used to designate sequenceor order of steps or importance. The terms “first” and “second” areinterchangeable, i.e., the heat exchanger (122) may be designated“first” and the heat exchanger (120) may be designated “second,”generally depending upon the order in which the heat exchangers aredescribed in this specification or recited in the claims.

As the combustion stream (104) is received in the SET chamber (108), thecombustion stream (104) is subject to cooling (or thermal transfer) bypassing the combustion stream (104) under the spray mechanism (118),which may be embodied as a nozzle, an atomizer, or other equipment forcontacting the liquid discharged by the spray mechanism (118) with theincoming combustion stream (104). The liquid, typically mostly or allwater, from the spray mechanism (118) condenses a portion or all of thegaseous water entrained in the incoming combustion stream (104) andoptionally acts as a scrubber to remove entrained particulate matter(e.g., soot) from the incoming combustion stream (104) and into theliquid (115). In an embodiment, substantially all of the gaseous waterentrained in the combustion stream (104) is condensed, such that theonly remaining water, if any, in the gas stream leaving the SET tank(108) via line (132) is due to the inherent vapor pressure of water inthe gas stream at its given temperature, for example, approximately 80°C. In an embodiment, the water entrained in the gas leaving the SET tank(108) via the line (132) is in the form of vapor as opposed to the waterin the inlet stream (104) that was in the form of saturated orsuper-heated steam. In an embodiment, additional water purificationsteps within the SET tank (108), such as before electrolysis (discussedbelow), are not required and may be omitted (but are not precluded).Transfer lines such the line (132) described above other lines describedbelow are also interchangeably referred to herein as conduits.

Water (or other liquid) emitted from the spray mechanism (118) and thewater condensed from the combustion stream (104) are collected at thelower part of the SET chamber (108), as represented in FIG. 1 by theliquid (115) and the water/liquid level line (116). In an embodiment,the incoming combustion stream (104) is cooled to about 80° C. by thewater or other liquid from the spray mechanism (118). In an embodiment,a portion of the water or other liquid emitted by the spray mechanism(118) is fed via a pump (130) and conduit (131) from the lower part ofthe SET chamber (108) into the methane separation chamber (110) forfurther use and processing, as described below.

The carbon dioxide and nitrogen of the combustion stream (104) aredischarged from the SET chamber (108) via the line (132). Accordingly,the carbon dioxide is thereby separated (204) from the water of thecombustion stream (104) in order to obtain relatively pure carbondioxide and nitrogen for later processing, including in certainembodiments absorption, desorption, and methanation, as discussed ingreater detail below. In an exemplary embodiment, the resulting gasmixture in the line (132) is substantially or fully dry or water free.In exemplary embodiments, the resulting gas mixture contains 0 to about3 weight percent water, 0 to about 2 weight percent water, or 0 to about1 weight percent water, or less than 0.1 weight percent water.Separation of the water entrained in the incoming combustion stream(104) from the carbon dioxide at an early stage in the system (100) andprocess (200) is desirable because the carbon dioxide is later subjectedto a methanation reaction (described below). Water, if not removed,would inhibit the methanation reaction, given that water is one ofreaction products of methanation, as shown the equation below. Thus,unremoved water (if any) that makes its way to the reactor pushes therate constant to the left and decreases the kinetic reaction rate.

(4H₂+CO₂=CH₄+2H₂O; ΔG=−3.7 kJ/g CO₂)

As mentioned above, in an exemplary embodiment electrolysis is carriedout in the SET chamber (108) using the anode (124) and the cathode (126)to generate hydrogen and oxygen (206). The anode (124) and the cathode(126) are shown operatively connected to the electrolysis systemcontroller (125), e.g., the electrically communicate with the controller(125). In non-limiting embodiments, the electrolysis equipment(124)-(126) may be, for example, part of an alkaline, PEM, or radio-waveelectrolysis system. Electrolysis uses electricity to split water in theSET chamber (108) into oxygen and hydrogen. The water used for theelectrolysis is supplied, in part or completely, from the exhaustcombustion stream (104), which acts as a feedstock for the electrolysis.The oxygen and hydrogen produced by electrolysis are discharged from theSET chamber (108) via lines (134) and (136), respectively. The lines(134) and (136), as well as other lines and conduits described herein,may be, for example, piping, hoses, tubes, etc. In an exemplaryembodiment, an example of which is discussed below with reference toFIG. 3 , neither the line (134) nor the line (136) leaving theelectrolysis cell pass through the fluid (e.g., water) (115) outside ofthe electrolysis cell. For example, in FIG. 3 , lines (334) and (336)(corresponding to lines (134) and (136), respectively, of FIG. 1 ) exitan electrolysis cell (305) above a liquid (e.g., water) level line (316)corresponding to liquid level line (116) of FIG. 1 .

In an embodiment, the production of hydrogen via electrolysis can beselectively throttled based on the supply of affordable electricity. Inan embodiment, the electrolysis system controller (125) is connected inreal-time via the Internet to real-time electricity markets and/or theperformance of distributed electricity generation equipment. Theconnected controller (125) is configured to decide, e.g., based onproject-specific economic parameters, whether to open or close anelectrical switch that manages the supply of electricity for carryingout the electrolysis.

According to an embodiment, the SET chamber (108) is operated inaccordance with a SET tank steady state equation as follows:

0={dot over (m)} _(s)(h _(in) −h _(out))_(s) +{dot over (Q)} _(elec){dot over (Q)} _(ex)+({dot over (m)}h)_(r,in)−({dot over (m)}h)_(r,out)+{dot over (m)} _(H2O,cond) ·h _(fg,H2O)

-   -   wherein {dot over (m)}_(s) is the mass flow rate of the solution        (H₂O+MEA) going into (164) the SET tank (108) and leaving (168)        the SET tank (108),    -   (h_(in)−h_(out))_(s) is the specific enthalpy difference of the        solvent before entering (164) and after exiting (168) the SET        tank (108),    -   ({dot over (m)})_(r,in) is the inlet mass flow rate of the        methanation products (144) (CH₄+2H₂O),    -   (h)_(r,in) is the inlet specific enthalpy of the methanation        products (144) (CH₄+2H₂O),    -   ({dot over (m)})_(r,out) is the mass flow rate of the methane        (146),    -   (h)_(r,out) is the specific enthalpy of the methane (146),    -   {dot over (m)}_(H2O,cond) is the mass flow rate of condensate        (114),    -   h_(fg,H2O) is the latent heat from H₂O condensation (114),    -   {dot over (Q)}_(ex) is the heat produced by the combustion        exhaust leaving the generator, boiler, or other example        combustion appliance (104), and    -   {dot over (Q)}_(Elec.) is the heat produced by the electrolysis.

As an example of a theoretical application of the SET tank steady stateequation, the following assumptions are made: (1) 10 kW petrolgenerator, boiler, etc. with 70% efficiency, 1.5 g/s exhaust gas flowrate, 15% carbon dioxide (CO2) mass fraction. (2) 100% CO2 capture andconversion into methane (CH4). (3) 10 kW electrolysis system cycle thatoperates 50% of the time, with 50% efficiency. Also, the followingconditions are assumed: (1) inlet solvent (164) temperature and pressureare 300K and 1.5 bar, respectively, and (2) outlet solvent (168)temperature and pressure are 360K and 1.5 bar, respectively (assumingzero pressure drop).

In a theoretical example, the SET tank steady state equation is solvedfor the mass flow rate of the solution entering (164) the SET tank asfollows:

${\overset{˙}{m}}_{s} = \frac{\left\lbrack {{\overset{˙}{Q}}_{elec} + {\overset{˙}{Q}}_{ex} + \left( {\overset{˙}{m}h} \right)_{r,{in}} - \left( {\overset{˙}{m}h} \right)_{r_{,}{out}} + \left( {{\overset{˙}{m}}_{{H2O},{cond}} \cdot h_{{fg},{H2O}}} \right)} \right\rbrack}{\left( {h_{out} - h_{in}} \right)_{s}}$

-   -   wherein

${{\overset{˙}{Q}}_{elec} = {\frac{10{{kW} \cdot 50}\%}{2} = {2.5{kW}}}};{{\overset{˙}{Q}}_{ex} = {\frac{10{kW}}{70\%} = {14.3{kW}}}};$

({dot over (m)})_(r,in) (623K, 1.5 bar)=0.27 g/sec; (h)_(r,in) (623K,1.5 bar)=2,754 kJ/kg; {dot over (m)}_(H2O,cond)=0.19 g/s;h_(fg,H2O)=2,200 kJ/kg; ({dot over (m)})_(r,out)=0.26 g/sec; (h)_(r,out)(300K, 1.5 bar)=1,419 kJ/kg; and reactor heat transfer=({dot over(m)}h)_(r,in)−({dot over (m)}h)_(r,out)+({dot over(m)}_(H2O,cond)·h_(fg,H2O))=0.7 kW;

${h_{out} = \frac{242{kJ}}{kg}};{h_{in} = {\frac{7kJ}{kg}.}}$

Solving for {dot over (m)}_(s),

${\overset{˙}{m}}_{s} = {\frac{\left\lbrack {{2.5{kW}} + {14.3{kW}} + {0.7{kW}}} \right\rbrack}{\left( {{242\frac{kJ}{kg}} - {7\frac{kJ}{kg}}} \right)_{s}} = {0.075\frac{kg}{s}}}$

In the embodiment illustrated in FIG. 1 , oxygen is fed via the line(134) to an oxygen storage tank (138). Alternatively, the line (134) maydeliver the oxygen back to the appliance (102), to another appliance(not shown), or may be used for other purposes. The hydrogen is fed viathe line (136) from the SET chamber (108) to a methanation pre-heater(140). A pressure transducer (or hydrogen sensor) (135) (the equivalentof Pressure trans 2 (520) in FIG. 5 and PT-2 (612) in FIG. 6 , discussedbelow), is positioned along the feed line (136) for measuring theoverall pressure in the line/reactor that is inclusive of all gases thatmay be present. As an example, the pressure may be in a range of 0 barto 10 bar. As a non-limiting example, 0.1 to 0.5 bar of negativepressure (less than 1 bar) may be used to aspirate the hydrogen out ofthe SET chamber (108). The pressure transducer (135) is labeled as an H₂sensor in FIG. 1 in order to reflect the typical operating conditions,where the only constituent within the conduit will be (or is assumed tobe) hydrogen and therefore a change in pressure will reflect a change inthe presence of hydrogen within the conduit.

If needed or desired, an additional amount of water (or “make-up water”)can be added to the SET chamber (108) from the methane separationchamber (110) via the injection conduit or port (114) to increase thehydrogen and oxygen production in the SET chamber (108). As mentionedabove in connection with the spray mechanism (118), a portion of thewater or other liquid in the methane separation chamber (110) isdelivered to the methane separation chamber (110) by the pump (130) andconduit (131). Another portion of the water or other liquid in themethane separation chamber (110) is supplied from a methanation reactor(142) via conduit (144), as will be described in greater detail below.The water in the methane separation chamber (110) is also referred toherein as condensate (121), which defines a condensate level line (123).

The conduit (144), e.g., one or more sealed tubes, carries methanationreaction products, including methane and gaseous water, into the SETchamber (108) and through the first heat exchanger (120) located in theSET chamber (108). The first heat exchanger (120) may be embodied as oneor more sealed pipes and/or coils carrying the methanation reactionproducts through the liquid (e.g., water) (115) in the SET chamber (108)to cause heat transfer from the methanation reaction products to theliquid (115). In another embodiment, known and other heat exchangers maybe used as the first heat exchanger (120). The methane reaction productsgenerally have a relatively high temperature, for example, in a range of150° C. to 450° C., compared to the water (115) in the SET chamber(108).

The transfer of heat from the reaction products in the conduit (144) tothe water or other liquid (115) in the SET chamber (108) facilitateselectrolysis (206), described above, and solvent heat (214) and carbondioxide desorption (216), described below. In an exemplary embodiment,electrolysis takes place at about 80° C. The methanation reactionproducts in the conduit (144) are cooled by the water (115) in the SETchamber (108), e.g., to about 80° C., and are delivered into the methaneseparation chamber (110). According to an embodiment, the conduit (144)delivers the methanation reaction products below the condensate levelline (123) of the condensate (121) of the methane separation chamber(110). According to another embodiment (not shown), the conduit (144)delivers the methanation reaction products above the condensate levelline (123) of the condensate (121), i.e., into the headspace (112) ofthe chamber (110).

Methane is separated (210) from the water and any particulate matter inthe methane separation chamber (110) via condensation of the water (andgravity), which forms the condensate (121). The separated methane isdelivered via conduit (146) to a methane storage tank (148). In anembodiment, the system (100) further includes a compressor configured topressurize the methane to an ideal storage pressure of, for example, asmuch as 200 bar, for delivery to the methane storage tank (148). Themethane gas may be stored in the methane storage tank (148) for a finiteperiod or an indefinite time period, such as long as multiple years, ifdesired or required. The methane that is produced may be storedindefinitely and has an energy density of, for example, more than 100times that of a typical lithium-ion battery, which makes the methane apractical medium for serving as the basis for an economy that runs 100%on renewable energy. The methane stored in the tank (148) may be burnedin the presence of air for various uses, including, without limitation,use in the combustion appliance (102), heat production, electricityproduction, or mechanical energy.

In an embodiment, the concentration (e.g., mass percent) of the carbondioxide in the conduit (132) is measured by a gas analyzer (150) beforethe carbon dioxide and nitrogen are fed into a carbon dioxide absorber(152). In an embodiment, the gas analyzer (150) is configured to useelectromagnetic wave profiles to determine carbon dioxide concentration(e.g., mass percent) in the gas stream within the conduit (132). Inembodiments, the measured carbon dioxide concentration may be used todetermine speeds of pumps and fans that drive the absorber (152) and adesorber, also referred to as a regenerator, (170) and/or measuring theoverall efficiency of carbon dioxide capture.

The carbon dioxide absorber (152) is operable to separate the carbondioxide from the nitrogen and any other gases (e.g., carbon monoxide),which if present, are typically in trace amounts. In an embodiment, thecarbon dioxide and nitrogen are injected in the carbon dioxide absorber(152) under a spray mechanism (e.g., a nozzle, atomizer, etc.) (154)that sprays a carbon dioxide solvent (delivered via (156), discussedbelow). In an exemplary embodiment, the spray mechanism (e.g., nozzle)(154) delivers the solvent as a fine mist. The carbon dioxide solvent iscombined with the carbon dioxide and nitrogen in order to capture (orabsorb) the carbon dioxide (212), in an exemplary embodiment tosaturation. Representative solvents for carbon dioxide capture include,for example, monoethanolamine (MEA), Selexol® (dimethyl ethers ofpolyethylene glycol (DEPG)), Fluor solvent (propylene carbonate),Purisol (N-methl-2-pyrrolidone), Rectisol (methanol), a sulfinol solvent(a mixture of diisopropanolamine or methyl diethanolamine (MDEA),sulfinol (containing sulfolane, tetrahydrothiophene dioxide and water),econamine FG (amine-based), and ionic liquids (e.g.,1-butyl-3-propylamineimidazolium tetrafluoroborate). In an exemplaryembodiment, the solvent comprises a sulfinol solvent or an equivalentsolvent. Temperature in the absorber (152) may be conducive to capturingthe carbon dioxide in the solvent. In an exemplary embodiment, atemperature of, for example, 20° C. is useful for carbon dioxidecapture, although room temperature and other temperatures may be used.

The resulting solvent with captured carbon dioxide falls via gravity tothe bottom chamber (158) of the absorber (152) where the solventcollects. In an embodiment, the relatively cool solvent is saturatedwith the carbon dioxide at this point. The nitrogen and any trace gasesin the absorber (152) are vented (162) from the top of the absorber(152) into the atmosphere or collected (not shown). Nitrogen is anon-polar diatomic molecule that typically does not chemically bind tothe solvent, whereas the carbon dioxide does, thus explaining why thenitrogen is not captured by the solvent falling into the bottom chamber(158) of the absorber (152). The mechanism for the capture of carbondioxide by the solvent is unique to each solvent. For example, in thecase of MEA, without wishing to be bound by any theory, the capturemechanism is believed to involve hydrogen bonding. Without wishing to bebound by any theory, in the case of the above-mentioned embodiment withsulfinol, the mechanism is related to the bonding between the hydrogenatoms in the sulfinol to the atoms in the carbon dioxide.

According to an embodiment, the carbon dioxide absorber (152) isoperated in accordance with the absorber energy balance equation asfollows:

0={dot over (Q)} _(Abs)+({dot over (m)}h)_(ex,in) +{dot over (m)}_(vap)(h _(in) −h _(out))_(vap) +{dot over (m)} _(s)(h _(in) −h_(out))_(s) +{dot over (m)} _(air)(h _(in) −h _(out))−({dot over(m)}h)_(N2,out)

-   -   wherein (h)_(ex,in) is the exhaust gas inlet enthalpy (132),    -   ({dot over (m)})_(ex,in) is the exhaust gas inlet mass flow rate        (132),    -   {dot over (m)}_(vap) is the mass flow rate of the CO₂+H₂O vapors        post the desorber and the outlet mixture after the dry cooler        (176),    -   (h_(in)−h_(out))_(vap) is the specific enthalpy difference        between the CO₂+H₂O vapors post the desorber (176) and the        outlet mixture after the dry cooler (186),    -   {dot over (m)}_(s) is the mass flow rate of the lean amine        (solvent inlet) (156) or the saturated amine (solvent outlet)        (164), which should be substantially equal to one another,    -   (h_(in)−h_(out))_(s) is the enthalpy difference between the lean        amine (solvent inlet) (156) and the saturated amine (solvent        outlet) (164),    -   {dot over (m)}_(air) is the mass flow rate of the inlet air or        the outlet air (187), which should be substantially equal to one        another, in the dry cooler (186),    -   (h_(in)−h_(out)) is the enthalpy difference between the inlet        air and the outlet air (187) in the dry cooler (186),    -   ({dot over (m)})_(N2,out) is the mass flow rate of the        non-captured gas (162) that leaves the absorber (152), and    -   (h) N_(2,out) is the specific enthalpy of the non-captured gas        (162) that leaves the absorber (152), and    -   {dot over (Q)}_(Abs) is the heat of absorption (152).

As an example of a theoretical application of the carbon dioxideabsorber equation, the following theoretical assumptions are made: (1)an adiabatic absorption tower as the absorber (152), (2) assume no heattransfer in the dry cooler (i.e., no difference in the captured gasenthalpy and the exhaust gas enthalpy), (3) heat generation is due toabsorption only, and (4) carbon dioxide capture flow rate is 0.5 g/s.Additionally, the following conditions are assumed: (1) inlet solventtemperature and pressure are 300K and 1.5 bar, respectively, (2) solventmass flow rate is 0.1 kg/sec, and (3) the heat of absorption is

$1820{\frac{kJ}{{kg} - {CO}_{2}}.}$

In a theoretical example, the absorber energy balance equation is solvedfor outlet solvent temperature as follows, wherein c p is the heatcapacity of the solvent:

$0 = {{\overset{.}{Q}}_{Abs} + {{\overset{.}{m}}_{s}\left( {h_{in} - h_{out}} \right)}_{s}}$$h_{out} = {{\frac{{\overset{.}{Q}}_{Abs}}{{\overset{.}{m}}_{s}} + h_{in}} = {{\frac{1820 \cdot 0.5 \cdot 10^{- 3}}{0.1} + {7\frac{kJ}{kg}}} = {16.1\frac{kJ}{kg}}}}$$T_{out} = {{T_{in} + \frac{\Delta h}{c_{p}}} = {{300 + \frac{16.1 - 7}{3.88}} = 302.34}}$

The relatively cool solvent, which in an exemplary embodiment issaturated or substantially saturated with the captured carbon dioxide,is directed out of the absorber (152) via conduit (164) by a pump (166).The solvent with captured carbon dioxide within the conduit (164), e.g.,sealed tube(s), is passed through the second heat exchanger (122) in theSET chamber (108). The second heat exchanger (122) may be embodied asone or more sealed pipes and/or coils carrying the solvent with capturedcarbon dioxide through the water (115) or other liquid in the SETchamber (108) to cause heat transfer. In another embodiment, known andother heat exchangers may be used as the second heat exchanger (122).The first and second heat exchangers (120) and (122), respectively, maybe a single (common) heat exchanger or different heat exchangers. Thesolvent with captured carbon dioxide is heated (214) in the SET chamber(108). In an exemplary embodiment, heat released by the methanationreaction products from the first heat exchanger (120) into the liquid(115) is used to heat the solvent with the captured carbon dioxide. Inan embodiment, the solvent with captured carbon dioxide is heated toabout 80° C. The heated solvent with the carbon dioxide are conveyed outof the SET chamber (108) along conduit (168) to the carbon dioxidedesorber (170).

In an embodiment of an operation of the carbon dioxide desorber (170),the heated solvent with captured carbon dioxide is sprayed through aspray mechanism (172), such as a nozzle, atomizer, etc., onto a mesh bed(174). In an embodiment, the mesh bed comprises a physical contactmaterials used in gas and/or liquid reactors to increase the surfaceavailable for absorption and/or chemical reactions. In an embodiment,the mesh bed is designed to possess high surface area and low pressuredrop characteristics and is made of a chemically inert material ormaterials. The carbon dioxide and water vapor, to the extent that anysuch vapor has been captured by the solvent, are released from theheated solvent due to the high temperature in a carbon dioxidedesorption or reclamation step (216), and are allowed to vent out of thecarbon dioxide desorber (170) through a conduit (176).

The carbon dioxide and vapor are pumped via a pump (178), which in anembodiment may be a fan or blower operating to maintain movement of thecarbon dioxide and any vapor, to a third heat exchanger (180). Theunsaturated hot solvent in the carbon dioxide desorber (170) falls viagravity to a bottom chamber (182) of the desorber (170).

According to an embodiment, the desorber (152) is operated in accordancewith the desorber energy balance equation below:

0={dot over (Q)} _(Des) +{dot over (m)} _(in) ^(Sat.) h _(in) ^(Sat)−{dot over (m)} _(out) ^(CO2) h _(out) ^(CO2) −{dot over (m)} _(out)^(MEA) h _(out) ^(MEA)

-   -   wherein {dot over (Q)}_(Des) is the heat consumed by desorption,    -   {dot over (m)}_(in) ^(Sat.) is the mass flow of saturated MEA        (or other solvent) solution entering (168) the desorber (170),    -   h_(in) ^(Sat) is the specific enthalpy of the saturated MEA (or        other solvent) solution entering (168) the desorber (170) at        87° C. and 1 bar,    -   {dot over (m)}_(out) ^(CO2)=the mass flow of the CO2 exiting        (176) the desorber (170),    -   h_(out) ^(CO2)=the specific enthalpy of the CO2 exiting (176)        the desorber (170) at 87° C. and 1 bar,    -   {dot over (m)}_(out) ^(MEA)=the mass flow unsaturated MEA (or        other solvent) leaving (156) the desorber (170), and    -   h_(out) ^(MEA)=the specific enthalpy of the MEA (or other        solvent) leaving (156) the desorber (170) at 87° C. and 1 bar.

As an example of a theoretical application of the desorber energybalance equation, the following assumptions are made: (1) an adiabaticdesorption tower, (2) assuming no carbon dioxide and vapor enthalpies(3) heat generation is due to desorption only, and (4) carbon dioxidecapture flow rate is 0.5 g/s. Additionally, the following conditions areassumed: (1) inlet solvent temperature and pressure are 360K and 1.5bar, respectively, (2) solvent mass flow rate is 0.1 kg/sec, and (3) theheat of absorption is

$1820\frac{kJ}{{kg} - {CO}_{2}}$

In a theoretical example, the desorber energy balance equation is solvedfor outlet solvent temperature as follows:

$0 = {{\overset{.}{Q}}_{Des} + {{\overset{.}{m}}_{in}^{Sat} \cdot h_{in}^{Sat}} - {{\overset{.}{m}}_{out}^{MEA}h_{out}^{MEA}}}$$h_{out}^{MEA} = {{{- \frac{{\overset{.}{Q}}_{Des} \cdot {\overset{.}{m}}_{out}^{{CO}2}}{{\overset{.}{m}}_{out}^{MEA}}} + h_{in}^{Sat}} = {{{- \frac{1820 \cdot 0.5 \cdot 10^{- 3}}{0.1}} + {242\frac{kJ}{kg}}} = {233\frac{kJ}{kg}}}}$

In FIG. 1 , a pump (184) transports the unsaturated hot solvent alongthe conduit (156) to a dry cooler (186) that forms part of or includesthe third heat exchanger (180). A gas circulator (187) is shownoperatively connected to the dry cooler (186) for transporting gas toand from the dry cooler (186) and the third heat exchanger (180). In anexemplary embodiment, the gas circulated by the gas circulator (187) isair. In an embodiment, the gas circulator (187) pulls room temperatureair from the surrounding embodiment, as needed or desired. The thirdheat exchanger (180) causes an exchange of heat between, on the onehand, the carbon dioxide and water vapor from conduit (176) and the hotunsaturated solvent from the conduit (156), and on the other hand, thecool gas (e.g., air) cycled through by the gas circulator (187). As thecarbon dioxide and water vapor cool, condensate from the water vapor iscollected in collection vessel (188). The solvent from the conduit(156), now cooled, is fed to and discharged through the nozzle (154) asdescribed above for again capturing carbon dioxide fed into the carbondioxide absorber (152) via the conduit (132).

The carbon dioxide is transported from the third heat exchanger (180)along conduit (190) to the methanation pre-heater (140). The conduit(190) carrying the carbon dioxide is shown equipped with a carbondioxide (CO₂) sensor (191). In an embodiment, the carbon dioxide sensor(191) measures the content (e.g., mass percentage or mass flow of CO₂)of carbon dioxide in the conduit (190). Excess carbon dioxide may bestored in a carbon dioxide storage tank (192) for later use, includinglater feeding to the methanation pre-heater (140).

The methanation pre-heater (140) includes fourth and fifth heatexchangers (194) and (196), respectively, for pre-heating (218) thehydrogen delivered via conduit (136) and the carbon dioxide deliveredvia conduit (190), respectively. In an embodiment, a thermal mass (198)serves as a heat source, delivering thermal energy (199) to the fourthand fifth heat exchangers (194) and (196), respectively. In an exemplaryembodiment, the thermal mass (198) is heated by the exothermic reactionthat takes place in the methanation reactor (142), as described infurther detail below. As shown in FIG. 1 , the thermal mass (198) ispositioned external to the methanation reactor (142) in accordance withthe illustrated embodiment. In another embodiment (not shown), thethermal mass (198) is positioned within or internal to the methanationreactor (142). In still another embodiment (not shown), first and secondthermal masses are respectively positioned internal and external to themethanation reactor (142). In an embodiment, the thermal mass (198)comprises a phase change material such as sodium nitrate (NaNO₃).

Carbon dioxide and hydrogen pre-heated by the methanation pre-heater(140) are introduced into the methanation reactor (142), where thecarbon dioxide and hydrogen react to generate combustible hydrocarbons,in particular at least methane, and water (220). A Sabatier reactor maybe used as the methanation reactor (142). In an exemplary embodiment,the reactor (142) is maintained at a temperature or temperatures in arange of 150° C. and 400° C., typically about 350° C. An appropriatecatalyst, such as nickel, may be used to initiate a Sabatier reaction toproduce the methane and water from the carbon dioxide and hydrogen.

In step (222), waste heat from methanation reactor (142) is recoveredand reused. In the illustrated system (100), the waste heat is conveyedvia line (197) to the thermal mass (198), which may be internal orexternal to the methanation reactor (142). In an embodiment, the thermalmass (198) is melted by the heat released by the exothermic reactionbetween carbon dioxide and hydrogen in the methanation reactor (142). Inan exemplary embodiment the methanation reactor (142) operates at aminimum temperature of 150° C., and typically operates at a temperatureof 350° C.

The high temperature methane and gaseous water generated in step (220)are discharged from the methanation reactor (142) via the conduit (144),which as described above enters the SET chamber (108) and the first heatexchanger (120) to provide heat for electrolysis and/or carbon dioxidedesorption, as represented in FIG. 2 by the return arrow from step (220)to step (208).

It should be understood that the illustrated system (100) of FIG. 1 maybe altered or modified in various manners. Additional conduits, pumps,sensors, valves, other equipment, etc. may be added to the system (100).Further, one or more conduits, pumps, sensors, valves, other equipment,etc. illustrated in FIG. 1 may be omitted from the system (100).Modifications may be made to the flow paths and arrangement of conduits,pumps, sensors, valves, other equipment, etc.

In an exemplary embodiment, part or all of the system (100), includingthe operation of the carbon dioxide absorber (152) and carbon dioxidedesorber (170), is continuous and carried out on a constant basis. Inother embodiments, parts or all of the system (100), such as methanation(220), may be carried out in batch mode.

In an exemplary embodiment, the system (100) is a closed loop thermaland hydrogen management system that integrates carbon dioxide captureand release, electrolysis, and methanation. In exemplaryimplementations, hydrogen is conserved and thermal energy is efficientlyused and recycled. In an exemplary implementation, pollution (e.g., theexhaust stream (104)) is converted into natural gas (methane) in aclosed-loop system creating a clean energy, zero-emission (or nearzero-emission) method, system, and apparatus.

An exemplary embodiment of a SET/separator tank suitable for the system(100) is generally represented in FIG. 3 by reference numeral (306).Like reference numerals are used for like parts between FIGS. 1 and 3 ,with the hundredths numeral “1” being changed to “3” for like parts ofFIG. 3 . Thus, the exhaust stream (104), SET/separator tank (106), SETchamber (108), methane separation chamber (110), partitioning wall(112), liquid (115), liquid level line (116), spray mechanism (118),first and second heat exchangers (120) and (122), condensate (121),condensate line (123), anode (124), cathode (126), pump (130), andconduits (131), (132), (134), (136), (144), (146), (164), and (168) arerepresented in FIG. 3 by reference numerals (304), (306), (308), (310),(312), (315), (316), (318), (320), (322), (321), (323), (324), (326),(330), (331), (332), (334), (336), (344), (346), (364), and (368),respectively. The first and second heat exchangers (120) and (122) ofFIG. 1 are combined and represented by a single heat exchanger(320)/(322) in FIG. 3 .

In an exemplary embodiment, an electrolysis cell (305) is positionedinside the SET chamber (308). A non-conductive separator (327) ispositioned within the electrolysis cell (305) to separate the electrodechambers holding the anode (324) and the cathode (326). The electrolysiscell (305) may also be provided with a non-conductive cell or envelope(329).

In an exemplary embodiment, the liquid, e.g., water (unnumbered) of theelectrolysis cell (305) is physically isolated from the remainder of thebulk fluid (315) inside the SET tank (308). The physical isolation ofthe liquid of the electrolysis cell (305) and the bulk fluid (315) ofthe SET tank (308) provides advantages of pH control and substantiallyisolating solid particulates inside the bulk fluid (315) of the SETchamber (308) from the electrolysis cell (305) (as discussed below inconnection with filter (317)). In an embodiment, installation ofmultiple (not shown) electrolysis cells inside the SET chamber (308) inthis manner establishes a manifold of multiple electrolysis cells suchthat a single high voltage power feed can be split and provide lowvoltage power to the individual electrolysis cells.

Excess bulk fluid (315) inside of the SET chamber (308) flows through afilter (317) into the electrolysis cell(s) as the liquid (e.g., water)is captured from the cooled combustion exhaust (304) and the methanationreaction products (334). In an embodiment, this configuration providesfor optimization of the thermal mass (e.g., the water or other liquid(115)) of the SET chamber (308) versus the electrolysis cells (e.g.,305) to ensure a thermally stable environment.

The pH of the electrolysis cell (305) may become lower as a result ofthe dilutive bulk fluid (e.g., water) (315) added from the SET chamber(308), e.g., through the filter (317). To maintain the pH at a desirablelevel, according to an embodiment a separate reservoir of highlyalkaline solution, such as potassium hydroxide (KOH), sodium chloride(NaCl), or one or more other electrolytes is fed to the electrolysiscell (305) as needed or desired to maintain a desirable pH. In anexemplary embodiment, pH is maintained at about 10.

According to an embodiment, the water level (316) in the SET chamber(308) is maintained via conservation of hydrogen atoms via reclamationof water from the methanation reaction products and the combustionexhaust, and makeup water added to the SET chamber (308) via a separatemakeup water line as needed or desired. In an embodiment, the waterlevel (316) in the SET chamber (308) is maintained at the level of theinlet/filter (317) to the electrolysis cell(s) (305) to ensure theelectrolysis cell(s) (305) have a constant supply of fluid (e.g., water)for producing hydrogen.

In an exemplary embodiment, the electrolysis electrodes (324) and (326)(or (124) and (126) in FIG. 1 ) are installed inside insulated lines,such as insulated hoses, so that the oxygen (O₂) and hydrogen (H₂)bubbles go naturally up the hoses and out of the electrolysis cell (305)via conduits (334) and (336), respectively, to their own isolatedchambers (not shown). Alternatively, the oxygen and hydrogen may berecycled or used for other purposes. For example, the conduit (336)carrying the hydrogen may be directed to a methanation pre-heater ormethanation reactor. In FIG. 3 , the conduits (334) and (336) eachinclude water traps (unnumbered, but shown as diamonds) that capturewater in a tank (337) for recycling back into the electrolysis cell(305) via a conduit (339).

An exemplary embodiment of an apparatus for carrying out the system(100) is generally represented in FIGS. 4A and 4B by reference numeral(400). Like reference numerals are used for like parts between FIGS. 1,4A, and 4B, with the hundredths numeral “1” used in FIG. 1 being changedto “4” for like parts of FIGS. 4A and 4B. Thus, the thermal mass (198),the pre-heater (140), the methanation reactor (142), the SET chamber(108), the methane separation chamber (110), the carbon dioxide desorber(170), and the carbon dioxide absorber (152) are represented in FIGS. 4Aand 4B by reference numerals (498), (440), (442), (408), (410), (470),and (452), respectively.

The apparatus (400) of FIGS. 4A and 4B comprises a plurality of chamberspositioned radially outside of one another, and in an exemplaryembodiment substantially concentric to one another. The thermal mass(498) is positioned at a center of the apparatus (400). The pre-heater(440) surrounds, and in an exemplary embodiment is substantiallyconcentric to, the thermal mass (498). The methanation reactor (442)surrounds, and in an exemplary embodiment is substantially concentricto, the pre-heater (440). A first or inner insulation layer (401) isinterposed between the methanation reactor (442) and the SET chamber(408), which surrounds, and in an exemplary embodiment is substantiallyconcentric to, the first or inner insulation layer (401). The SETchamber (408) is surrounded by, and in an exemplary embodimentsubstantially concentric to, the methane separator (410), which issurrounded by, and in an exemplary embodiment substantially concentricto, the carbon dioxide desorber (470). A second or outer insulationlayer (403) surrounds, and in an embodiment is substantially concentricto, the carbon dioxide desorber (470). The carbon dioxide absorber (452)surrounds, and in an exemplary embodiment is substantially concentricto, the second or outer insulation layer (403).

According to an embodiment, the temperatures of the chambers increasesin a direction annularly inward, i.e., so that the hottest chambers areat or near the center of the apparatus (400) (e.g., the thermal masschamber (498)) and the coolest chambers are at or near the outerperiphery of the apparatus (400) (e.g., the carbon dioxide absorberchamber (452)).

The apparatus (400) of FIGS. 4A and 4B illustrates the architecture,functionality, and operation of a possible implementation of systems andmethods described herein. In some alternative implementations, thearrangement of chambers in the apparatus (400) may be repositioned(e.g., transposed, switched) with respect to one another, depending uponthe functionality involved. Two or more chambers shown substantiallyconcentrically arranged may be combined and embodied as a singlechamber. Alternatively, single chambers may be divided into multiplechambers, e.g., multiple concentric chambers, relative to theillustrated embodiment of the apparatus (400) of FIGS. 4A and 4B. One ormore of the chambers of the apparatus (400) may be omitted. One or moreadditional chambers not shown in FIGS. 4A and 4B may be added to theapparatus (400). The first and second insulation layers (401) and (403),respectively, may be positioned at other locations than shown oromitted. Additionally insulation layers not shown in FIGS. 4A and 4B maybe added to the apparatus (400) between any of the chambers and/oraround the outside of the apparatus (400).

In an embodiment, the design of the apparatus (400) permitsimplementation of all or part of the system (100) and operation of allor part of the method (200) within a cylindrically constructedapparatus. The apparatus (400) may be scaled as needed or desired.According to a non-limiting embodiment, the apparatus (400) issufficiently compact to fit through a standard 2.5 foot (0.762 m)×7 foot(2.13 m) doorway.

FIG. 5 is a schematic diagram of a methanation system (500) according toan embodiment, and FIG. 6 is a flowchart (600) for operation of themethanation system (500) of FIG. 5 . FIGS. 5 and 6 are applicable to thebatch operation of a reactor (502), such as a Sabatier reactor. Itshould be understood that the following steps and operation are providedby way of example and are not limiting. For example, in alternativeembodiments a Sabatier reactor may be operated in a continuous processmanner.

-   -   1. The reactor (502) is heated (602) to a predetermined        temperature suitable for carrying out methanation by heating the        catalyst within the reactor (502). In an embodiment, heating may        be carried out via an electric resistance coil. A thermocouple        (504) is used for temperature measurement and collection of        data. If a determination (604) is made that a predetermined        temperature value has not been reached, heating continues. If a        determination (604) is made that the predetermined temperature        value has been reached, the process continues to step (606).    -   2. In step (606), ball valves V₁ (506) and V₂ (508) are turned        on (i.e., opened) and a vacuum pump (510) operates to vacuum        conduits connected to the vacuum pump (510) and a chamber (512)        of the reactor (502). For automatic opening and closing of        valves V₁ (506) and V₂ (508), low voltage solenoid relay valves        operating in a range of 0 to 5 Volts may be used. In an        embodiment, industrial control valves are operated at high        voltage input. A determination (608) is made whether a first        predetermined pressure (e.g., above 1 bar, such as 1.1 bar) as        measured by a pressure transducer (trans 1) (514) has been        reached inside the reactor (512). If the determination (608) is        answered in the negative, the vacuum pump (510) continues to        operate.    -   3. When the determination (608) is made that the pressure        transducer (trans 1) (514) has achieved the predetermined        pressure, the vacuum pump (510) stops, and the ball valves V₁        (506) and V₂ (508) are turned off (i.e., closed), and ball valve        V₃ (516) is turned on (610) (i.e., opened). According to an        embodiment, predetermined pressure valves (e.g., 1 Pascal or 10        Pascal) may be used for any or all valves, e.g., (506), (508),        (516), (522), and/or (526). Although ball valves are shown and        described herein, it should be understood that other types of        valves may be used.    -   4. After the valve V₃ (516) is turned on (i.e., opened) (610),        and the reactor (502) fills with hydrogen supplied by hydrogen        generator (518) until a determination (612) is made that the        pressure transducer (trans 2) (520) has achieved, e.g., exceeds,        a predetermined pressure value, according to mass stoichiometry.    -   5. In step (614), the valve V₃ (516) is turned off (i.e.,        closed) and valve V₄ (522) is turned on (i.e., opened). The        reactor (502) fills with carbon dioxide from carbon dioxide        source (524) until a determination (616) is made that the        Pressure Trans 2 (520) achieves a predetermined pressure value,        according to mass stoichiometry.    -   6. The valve V₄ (522) is turned off (i.e., closed) (618), so        that at this point, all of the valves V₁ (506), V₂ (508), V₃        (516), and V₄ (522) are off. Valve V₅ (526) is turned on (i.e.,        opened) (618). A gas pump (526) circulates samples from the        reactor (502) and the carbon dioxide percentage is measured by a        carbon dioxide sensor (532).    -   7. When a determination (620) is made that a predetermined        carbon dioxide percentage value (as measured by the CO₂ sensor        (532)) is achieved, a three-way valve (530) is opened and the        gas pump (528) aspirates the gas mixture (622) from the reactor        (502) by adjusting the position of the three-way valve (530)        such that the gas mixture may leave the reactor (502) and the        connected piping (534). After this step, the reactor (502) is        ready for another batch operation, at which point the three-way        valve (530) is adjusted to prevent the gas mixture from leaving        the piping (534) connected to the reactor (502) and instead        causes the gas mixture to circulate between the reactor (502)        and the CO₂ sensor (532).

An Electrolysis Controller Equation: In an embodiment, a decisionwhether or not to run the electrolysis system and produce hydrogen inthe SET chamber/tank is driven by balancing the price of electricity,the price of natural gas, and the pressure of the methanation reactor,that is, if the methanation reactor and its associated preheater aredepressurized such that the reactor and preheater are capable ofreceiving hydrogen that is produced.

In an exemplary embodiment, the incorporation of the electrolysis systemwithin the SET tank creates a thermally stable environment for the rapidon/off operational cycle of the electrolysis system, where heat transferwithin the SET tank (e.g., from the methanation products to thesaturated solvent and liquid (e.g., water) in the SET tank (108)) isregulated based on whether the electrolysis system is activated.Regulation may include controlling the flow rate of the saturatedsolvent stream (164), e.g., slower solvent flow rates increase heattransfer. The specified Electrolysis Controller Equation is implementedin an embodiment described herein as a result of the SET tank/chamberenvironment for the electrolysis system and the batch operational modeof the methanation reactor. In an embodiment, the ElectrolysisController Equation prescribes rapid on/off cycles. The batchmethanation reactor accommodates the sporadic nature, if any, of thehydrogen production and the SET tank accommodates any sporadic heatoutput of the electrolysis system.

In an embodiment, rapid venting of the hydrogen into the methanationpre-heater (140) prevents a buildup of products around the electrodes,which would impede the hydrolysis reaction. This is expressedmathematically as follows:

-   -   E1=ON=>Electrolysis is active and producing hydrogen/oxygen        inside the SET tank,

If (the total value of methane produced>the total value of electricitypurchase AND the pressure sensor on the H2 generator outlet, S2<1 bar=>,THEN active depressurization of the methanation reactor to prepare forreceipt of hydrogen and carbon dioxide).

-   -   E1=OFF=>Electrolysis is inactive and not producing hydrogen and        oxygen inside the SET tank.

Natural Gas Valuation: In an embodiment, the total value of methaneproduced is variable based on the market conditions for both electricitypurchased and methane sold. For example, if the user selects on thesystem control for natural gas to be sold on the open market, and theuser is able to sell natural gas into a renewable natural gas market,then the system control will reach the daily renewable natural gas priceand that will be the value of the natural gas produced. In anembodiment, natural gas produced by the system is only certified as“renewable” if the electricity used for electrolysis derives from arenewable source, such as solar panels, wind turbines, etc. In anembodiment, if the electrolysis system is connected directly to a sourceof renewable electricity, then the natural gas produced will be rated asrenewable. On the other hand, if the electrolysis system is connected tothe grid, then the electrolysis system will treat the electricityinputted as from a mixed source proportional to the electricity on thegrid at the time of operation per the specifications of the gridoperator. The above implementations relating to natural gas valuationare provided by way of example only, and are not limiting.

For example, FIG. 7 shows the readout of an electrolysis systemoperating in NYS at the time shown. The embodiment illustrated in FIG. 7depicts a makeup of electricity generator sources at a specific time.For example, electricity consumed at the time captured by FIG. 7 isabout 23% nuclear derived.

Only about 21% (i.e., 2% wind, 18% hydro, and 1% other renewable) of theelectrolysis system of FIG. 7 is considered as being fed from arenewable source and thus 21% of the natural gas produced would be ratedas renewable, and the remainder of the produced natural gas would berated as non-renewable.

The value of the natural gas produced would in turn be the blended priceof the renewable natural gas and non-renewable natural gas prices,assuming the natural gas is set to be sold on the market accordingly. Inan embodiment, in the event the natural gas is contracted to be sold ata fixed price then that valuation is applied.

In an embodiment, in the event that the natural gas produced is set to anet meter where the facility operates the existing natural gas meter inreverse and provides a credit, then the valuation of the natural gas isset to be the all-in supply+delivery+taxes cost of the natural gaspreviously purchased at the facility on the condition that natural gaswas previously purchased within the appropriate billing period to avoidcharges. If there was no natural gas previously consumed within thebilling period then the natural gas would be valued at whatever pricethe natural gas utility charges for gas fed to the grid.

Electricity Valuation: In an embodiment, the value of the electricitysupplied to the electrolysis process is either a fixed cost applied tothe system controller connected to the grid or the value is a functionof the rates, tariffs and locational based pricing for the 5 minuteinterval of pricing applied at the time of consuming electricity. Forexample, if the electricity is to be purchased in NYS Zone J is$44.17/MWh, then the commodity price of the electricity prior to addingany additional utility based charges would be $44.17/MWh and this valuewould change every 5 minutes.

In an embodiment, the electrolysis controller (125) is designed tointerface with all natural gas markets and utilities to account for allof the above scenarios when providing a valuation of the natural gasthat is produced.

SET Tank Controller Equation: In exemplary embodiments, the SET tank ismaintained at 80° C.

In embodiments, there may be one or more sources for heating the SETtank. In an embodiment, the only source of cooling the SET tank is thesolvent pump (166) that feeds rich cold solvent via a heat exchangerthrough the SET tank in order for the solvent to be heated and theliquid (e.g., water) in the SET tank to be cooled. The tandem pump topump P1 (166) is the pump P2 (184), which takes hot lean solvent fromthe desorber. In an embodiment, the speed and size of the pump P2 (184)is maintained equal to the speed and size of the pump P1 (166) in orderto maintain a mass balance on the solvent in the system.

In an embodiment, the size of the pump P1 (166) is set such that it maynormally operate at a relatively low speed of 30% of its capacity butwhen operating at 100% of its capacity has the ability to providecooling capacity that can match the heat output of the SET tank when allsources of heat in the SET tank (e.g., electrolysis, combustion exhaust(104), and methanation reactor outlet (144)) are at their maximumpotential.

In an embodiment, the operation of the pump P1 (166) is also influencedby the carbon dioxide percent at the outlet of the absorber (152). Forexample, in an embodiment the speed of the pump P1 (166) is increased inorder to ensure the carbon dioxide percent at a CO2 sensor (not shown inFIG. 1 ) installed on the N₂ exhaust conduit (162) is equal to zero.

Thus the mathematical description of the control of the pump P1 (166)according to an embodiment is as follows, where the CO₂ sensor “S1” isinstalled on conduit (162) in FIG. 1 :

Speed of the pump P1=f(SET-tank temperature, S1-CO2%)

wherein in an embodiment the pump P1 increases/decreases its speed inorder to maintain:

-   -   SET tank temperature<81 C    -   S1 CO2%=0

The Tables 1 and 2 below set forth non-limiting examples of assumptionsbased on calculations system performance for hypothetical technicalspecifications and system interconnections according to an embodiment.

TABLE 1 Technical Specifications Generator Rated 250 kW 500 kW 1 MWElectrical Output System Dimensions 3.01 × 2.35 × 2.36 m 5.89 × 2.35 ×2.36 m 12.03 × 2.4 × 2.36 m (16 m³) (33 m³) (67.7 m³) CO₂ Capture Rate500 1,000 2,000 [Tonnes/Year] Peak Electric Power 3.5 7 14 Input [MW]Continuous Electric 50 100 200 Power Input [kW] Synthetic Natural Gas9,338 18,767 37,352 Output [MMBtu/Year] Renewable Electricity 4,3298,658 17,316 Consumption [MWh/Year] Net System 64% 64% 64% Efficiency(Lower Heating Value Basis) Synthetic Natural Gas 179.96 359.91 719.82Storage Capacity [MMBtu]

TABLE 2 System Interconnections Electrical Connection AC 460 V | 3 PH AC460 | 3 PH AC 460 | 3 PH Option A 25,000 Amps 50,000 Amps 100,000 AmpsElectrical Connection AC 460 V | 3 PH AC 460 V | 3 PH AC 460 V | 3 PHOption B 5,000 Amps + 10 MW 5,000 Amps + 20 MW 5,000 Amps + 40 MW DCInput DC Input DC Input Tap Water 0.5 inch 0.5 inch 0.5 inch ConnectionSewer Water   1 inch   1 inch   1 inch Connection

Embodiments described above utilize a Sabatier reactor and process in ascalable manner so that various sources of carbon dioxide (e.g.,combustion appliance (102)) may be retrofitted with equipment embodiedherein in order to use intermittent renewable electricity to convertcarbon dioxide and water emissions into methane. A result is anembodiment in which an existing fossil-fuel fired combustion appliancemay be turned into a 100% carbon neutral system that maintains a closedloop on carbon.

In an exemplary embodiment, all or substantially all of the hydrogengenerated during electrolysis is fed to the methanation reactor, inwhich a catalytic reaction may proceed at high temperature, e.g., about350° C. In an exemplary embodiment, all or substantially all of thehydrogen is burned in the methanation reaction substantially immediatelyor instantaneously after the hydrogen has been generated. In exemplaryembodiments, the purity of the hydrogen does not need to be very high,which contrasts embodiments described herein against commercialprocesses requiring hydrogen purity of 99% or greater. In an embodiment,gases present with the hydrogen are burned as well. Thus, the gas flowinto the methanation reactor may be well below 99% purity, for example,on the order of about 70 mass percent hydrogen and 30 mass percent othergases. In exemplary embodiments, the ability to process hydrogen streamshaving relatively low purities provides greater design flexibility thatother hydrogen generator manufacturing systems lack.

In exemplary embodiments, energy efficiency considerations may similarlydiffer from those generally practiced in commercial processes. Whilehigh efficiency is desirable, embodiments described herein may bepracticed at lower electrolysis efficiencies of, for example, about 50%while still operating the overall system at a high efficiency. In thecommercial market, the incremental manufacturing costs to achieve purehydrogen and high electrolysis efficiencies are extremely large. It isthe difference between using lesser expensive equipment (e.g., commoditystainless steel components) versus more expensive equipment (e.g.,expensive platinum catalysts and/or rare earth elements etc.).Accordingly, embodiments described herein provide for capital costsavings by allowing for the use of lesser expensive equipment becausehigh purity hydrogen generation is not required.

Embodiments disclosed herein are directed to systems, apparatuses, andmethods configured to achieve, in particularly exemplary embodiments, atleast one of the following objects and advantages. First, combustionemissions, such as from a hydrocarbon combustion appliance or system,are isolated, reclaimed, and reused. In an exemplary embodiment, carbondioxide isolated from the combustion emissions and hydrogen generatedfrom water of the combustion emissions are converted into hydrocarbons,such as methane via methanation. Second, heat generated by methanationcan be utilized in other parts of the process, apparatus, and system,such as in the SET tank to drive the electrolysis and/or heat thesolvent containing captured carbon dioxide delivered from the carbondioxide absorber before the solvent is forwarded to the carbon dioxidedesorber. Third, water from the combustion emissions can be separatedand electrolyzed in an efficient manner for the purpose of generatinghydrogen for the methanation reaction. Fourth, the methane can berecycled back into a power plant or other system for further use and/orcan be put to other uses.

It should be understood that the process is scalable, including, forexample and not by limitation, from a 5 kW residential backup generatorto a 500 MW or greater capacity power plant.

In a particularly advantageous embodiment, the method and system may beintegrated with one or more natural energy sources, such as photovoltaicsolar cells, to operate equipment of the system and carry out steps ofthe method. For example, photovoltaic energy may be used to power theelectrolysis, the dry cooler, the compressor for methane compression,pumps, fans, control systems, peripheral loads, or any combinationthereof. In an exemplary embodiment, the method and system are practicedwithout the use of fossil fuels.

Certain embodiments disclosed herein efficiently integrate thermalseparation of water and chemical capture/absorption of carbon dioxide toseparate carbon dioxide from other constituents of an exhaust stream,including but not limited to water and nitrogen.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any claim unless recited in the claim.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, system, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,system, or apparatus. Also, the use of “a” or “an” are employed todescribe elements and components described herein. This is done merelyfor convenience and to give a general sense of the scope of thedisclosure. This description should be read to include one or at leastone and the singular also includes the plural unless it is obvious thatit is meant otherwise. If a specific number of an introduced claimelement is intended, such intent will be explicitly recited in theclaim, and in the absence of such recitation no such limitation ispresent. For a non-limiting example, as an aid to understanding, to theextent that the following appended claims contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimelement, the use of such phrases should not be construed to imply thatthe introduction of a claim element by the indefinite articles “a” or“an” limits any particular claim containing such introduced indefinitearticle and claim element to embodiments containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an”;the same holds true for the use in the claims of definite articles.

The various components and features of the above-described exemplaryembodiments may be substituted into one another in any combination. Itis within the scope of the invention to make modifications necessary ordesirable to incorporate one or more components and features of any oneembodiment into any other embodiment. One skilled in the art, using thedisclosures provided herein, will appreciate that various steps of themethods can be omitted, rearranged, combined, supplemented withadditional steps, and/or adapted in various ways. For example, in one ormore embodiments an alternative carbon dioxide capture and releasetechnique may be employed, such as but not limited to physicaladsorption.”

The foregoing description of the exemplary embodiments and exemplarymethods has been provided for the purpose of explaining principles ofthe invention and its practical application, thereby enabling othersskilled in the art to understand the invention for various embodimentsand with various modifications as are suited to the particular usecontemplated. The description is not necessarily intended to beexhaustive or to limit the invention to the precise embodimentsdisclosed.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, apparatuses, and methods according to various embodiments ofthe present embodiments. In some alternative implementations, thefunctions noted in the blocks may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved.

It will be appreciated that, although specific embodiments have beendescribed herein for purposes of illustration, various modifications maybe made without departing from the spirit and scope of the embodiments.Accordingly, the scope of protection of the embodiments is limited onlyby the following claims and their equivalents.

What is claimed is:
 1. A system comprising: a chamber configured tocontain liquid water and to receive a hydrocarbon combustion exhauststream comprising water and carbon dioxide; a heat exchanger positionedin the first chamber and configured to convey methanation reactionproducts through the chamber to transfer heat from the methanationreaction products to the liquid water; and an electrolysis systemconfigured to subject the heated liquid water to electrolysis togenerate hydrogen and oxygen, the electrolysis system comprising ananode and a cathode each received in the chamber.
 2. The system of claim1, further comprising: a second heat exchanger positioned in the chamberconfigured to heat solvent and carbon dioxide captured in the solvent,wherein the first and second heat exchangers comprise a common heatexchanger or different heat exchangers; and a separator configured toseparate at least a portion of the carbon dioxide from the heatedsolvent.
 3. The system of claim 2, further comprising: a carbon dioxideabsorber configured to capture the carbon dioxide in the solvent; and acarbon dioxide desorber configured to separate the at least a portion ofthe carbon dioxide from the heated solvent.
 4. The system of claim 3,wherein: the carbon dioxide desorber is configured to discharge a firststream comprising the carbon dioxide and a different second streamcomprising the heated solvent; and the carbon dioxide desorber isconfigured to cool the first and second streams.
 5. The system of claim3, wherein the carbon dioxide absorber is positioned substantiallyconcentrically outside of the carbon dioxide desorber.
 6. The system ofclaim 2, further comprising a methanation reactor configured to react atleast the hydrogen generated by the electrolysis and the carbon dioxideseparated from the heated solvent to generate the methanation reactionproducts.
 7. The system of claim 6, further comprising: a thermal massconfigured to be heated with heat generated by the reacting of at leastthe hydrogen and the carbon dioxide in the methanation reactor; and apreheater configured to preheat the hydrogen generated by theelectrolysis and the carbon dioxide separated from the heated solvent,the preheater being further configured to be heated with the thermalmass.
 8. The system of claim 7, wherein the methanation pre-heater ispositioned substantially concentrically within the methanation reactor.9. The system of claim 7, further comprising: a carbon dioxide absorberconfigured to capture the carbon dioxide in a solvent; and a desorberconfigured to separate at least a portion of the carbon dioxide from theheated solvent.
 10. The system of claim 9, wherein: the methanationreactor is positioned substantially concentrically outside of themethanation pre-heater; the first chamber is positioned substantiallyconcentrically outside of the methanation pre-heater; the carbon dioxidedesorber is positioned substantially concentrically outside of the firstchamber; and the carbon dioxide absorber is positioned substantiallyconcentrically outside of the carbon dioxide desorber.
 11. The system ofclaim 1, further comprising a second chamber that is different than thefirst chamber, the second chamber being configured to separate methanefrom the water of the methanation reaction products.
 12. The system ofclaim 11, wherein the first chamber and the second chamber are containedin a common tank.
 13. The system of claim 12, wherein the second chamberis positioned substantially concentrically outside of the first chamber.14. The system of claim 1, wherein the first chamber is configured tocondense at least a portion of gaseous water in the hydrocarboncombustion exhaust stream to add to the liquid water in the firstchamber.
 15. A system comprising: a chamber configured to subject liquidwater to electrolysis to generate hydrogen and oxygen; a carbon dioxideabsorber configured to capture carbon dioxide in a solvent; a first heatexchanger positioned in the chamber and configured to convey the solventand the captured carbon dioxide through the chamber; and a second heatexchanger positioned in the chamber and configured to convey methanationreaction products through the chamber to transfer heat from themethanation reaction products to the liquid water in the chamber and tothe solvent conveyed through the first heat exchanger of the chamber,wherein the first and second heat exchangers comprise a common heatexchanger or different heat exchangers.
 16. The system of claim 15,further comprising: a carbon dioxide desorber configured to separate atleast a portion of the carbon dioxide from the heated solvent.
 17. Thesystem of claim 16, wherein the carbon dioxide desorber is positionedsubstantially concentrically outside of the first chamber, and whereinthe carbon dioxide absorber is positioned substantially concentricallyoutside of the carbon dioxide desorber.
 18. The system of claim 15,wherein the chamber comprises a first chamber, and wherein the systemfurther comprises a different second chamber configured to separatemethane from water of the methanation reaction products.
 19. The systemof claim 18, wherein the second chamber is positioned substantiallyconcentrically outside of the first chamber.
 20. A system comprising: achamber configured to contain liquid water and to receive a hydrocarboncombustion exhaust stream comprising water and carbon dioxide; a firstheat exchanger positioned in the chamber and configured to conveymethanation reaction products through the chamber to transfer heat fromthe methanation reaction products to the liquid water; an electrolysissystem comprising an anode and a cathode positioned in the chamber,electrolysis system configured to generate hydrogen and oxygen from theheated liquid water; a carbon dioxide absorber configured to capture thecarbon dioxide in a solvent; a second heat exchanger positioned in thefirst chamber and configured to heat the solvent and the captured carbondioxide with thermal energy from the methanation reaction products,wherein the first and second heat exchangers comprise a common heatexchanger or different heat exchangers; a carbon dioxide desorberconfigured to separate at least a portion of the carbon dioxide from theheated solvent; and a methanation reactor configured to react at leastthe hydrogen generated by the electrolysis system and the carbon dioxideseparated from the heated solvent to generate one or more hydrocarbons.